Optical glass suffering little change in refractive index by radiation of light

ABSTRACT

An optical glass wherein an amount of change in refractive index (Δn: difference in refractive index between a state before radiation and a state after radiation) caused by radiation of laser beam at wavelength of 351 nm having average output power of 0.43 W, pulse repetition rate of 5 kHz and pulse width of 400 ns for one hour is 5 ppm or below is provided. The optical glass comprises a fluorine ingredient and/or a titanium oxide ingredient and/or an arsenic oxide ingredient. The optical glass suffers little change in refractive index by radiation of strong light having wavelengths of 300 nm to 400 nm such as ultraviolet laser.

This application is a division of Ser. No. 09/872,842, filed Jun. 1,2001 now U.S. Pat. No. 7,196,027, which claims priority from JapaneseApplication Ser. No. 2000-167377, filed Jun. 5, 2000 and JapaneseApplication Ser. No. 2000-330066, filed Oct. 30, 2000.

BACKGROUND OF THE INVENTION

This invention relates to an optical glass used in the near ultravioletregion and, more particularly, to an optical glass which suffers littlechange in refractive index by radiation of strong light havingwavelengths of 300 nm to 400 nm (e.g., super high pressure mercury vaporlamp and ultraviolet laser).

As an optical system using near ultraviolet rays, known in the art is anoptical lithography for exposing and copying a fine pattern of anintegrated circuit on a wafer such as a silicon wafer, i.e., an exposuredevice called i-line stepper using the i-line (365 nm) of a super highpressure mercury vapor lamp. In this exposure device, there is anincreasing tendency to expanding the exposure area with increase inintegration in LSI. In an optical system of the i-line stepper, lenseshaving a diameter of 200 mm or over is generally used. The optical glassfor i-line used for these lenses are required to have very highhomogeneity, to have internal transmittance for i-line of 99% or over inglass having thickness of 10 mm and to be free from deterioration due toultraviolet radiation, i.e., solarization.

For this reason, the optical glasses for i-line are produced on thebasis of established technique including adoption of high puritymaterials including little impurities, use of cleaner steps for mixingand melting of materials and removal of strain by highly-homogeneousmelting and precision annealing.

However, as integration of LSI tends to increase further, it is desiredfor the i-line stepper to have improved exposure and copyingcapabilities and durability over a long period of time and opticallenses used for the i-line stepper are desired to have high homogeneity,high transmittance, resistivity to solarization and also resistivity tothe i-line radiation, namely little change in refractive index by i-lineradiation.

As to change in refractive index by radiation of light, there is aphenomenon called the compaction phenomenon in which synthetic quartzglass undergoes changes in transmittance and density by radiation ofexcimer laser beam of a high level over a long period of time withresulting change in refractive index and the shape of glass surface.

The synthetic quartz glass is produced by synthesizing silicon oxide inthe form of fine powder by burning silicon tetrachloride withoxyhydrogen flame and sintering this silicon oxide powder by heating itat a high temperature. That is, it is synthesized by the reaction:SiCl₄+2O₂+4H₂→SiO₂+4HCl+2H₂O

The compaction phenomenon is considered to occur due to ions (OH⁻ andH⁺) derived from water content remaining in the synthesized quartz glassand/or cutting of the Si—O bond caused by incompleteness of reaction.

In the optical glasses for i-line offered for the i-line radiation,occurrence of the compaction phenomenon has not been specifically known.

It has unexpectedly been found that, in the optical glass for i-line,deterioration in homogeneity due to change in refractive index andincrease in strain, and deformation in the shape of the glass surfacetake place, in the same manner as was known in synthetic quartz glass,in a portion where ultraviolet ray or laser beam of a high level withinthe wavelength range from 300 nm to 400 nm has been radiated and,therefore, the optical glass for i-line does not possess sufficientresistivity to light. An optical system using such optical glasses,therefore, tend to produce deterioration in image quality which willcause a problem in further increase in integration of LSI andimprovement in the exposure and copying capabilities of the i-linestepper.

For example, PBL1Y which is an optical glass for i-line made by Ohara K.K. has undergone change in refractive index (Δn) of Δn=+9.0×10⁻⁶ in aportion where laser beam having wavelength of 355 nm has been radiatedby a Q-switch pulse solid laser under conditions of output of 1.2 W,beam diameter of 2.6 mm, radiation time of 3 hours and total pulsenumber of 5.4×10⁷ pulses.

It is, therefore, an object of the present invention to provide anoptical glass having excellent resistivity to change by radiation oflight in which change in refractive index caused by radiation ofultraviolet ray or laser beam of a high level having wavelengths withina range from 300 nm to 400 nm is restrained.

SUMMARY OF THE INVENTION

Studies and experiments made by the inventors of the present inventionfor achieving the above described object of the invention have resultedin the finding, which has led to the invention, that addition offluorine ingredient and/or titanium oxide ingredient and/or arsenicoxide ingredient as a glass component unexpectedly has an effect ofrestraining change in refractive index by radiation of light. Morespecifically, a glass which suffers little change in refractive index byradiation of ultraviolet ray can be obtained by (1) in a SiO₂—PbO-alkalimetal oxide glass, addition of a relatively small amount of fluorineingredient, and/or addition of As₂O₃ ingredient as a refining agentinstead of Sb₂O₃ ingredient, and/or addition of TiO₂ ingredient theamount of which is so small that influence to transmittance can beignored, (2) in a SiO₂—B₂O₃-alkali metal oxide and/or an alkaline earthmetal oxide glass, addition of fluorine ingredient, and/or addition ofAs₂O₃ ingredient as a refining agent instead of Sb₂O₃ ingredient, and/oraddition of TiO₂ ingredient the amount of which is so small thatinfluence to transmittance can be ignored and (3) in aP₂O₅—Al₂O₃-alkaline earth fluoride glass, non-addition of a refiningagent and TiO₂ ingredient, or addition of a very small amount of atleast one of these ingredients.

For achieving the above described object of the invention, there isprovided an optical glass wherein an amount of change in refractiveindex (Δn: difference in refractive index between a state beforeradiation and a state after radiation) caused by radiation of laser beamat wavelength of 351 nm having average output power of 0.43 W, pulserepetition rate of 5 kHz and pulse width of 400 ns for one hour is 5 ppmor below.

In one aspect of the invention, the optical glass comprises a fluorineingredient, and/or a titanium oxide ingredient, and/or an arsenic oxideingredient.

In another aspect of the invention, the optical glass comprises, in mass%, a total amount of 0.1-45% of F in one or more fluorides as thefluorine ingredient, and/or 0.001-0.5% of TiO₂ as the titanium oxideingredient, and/or 0.001-1% of As₂O₃ as the arsenic oxide ingredient.

In another aspect of the invention, the optical glass comprises, in mass%,

SiO₂ 40-70% PbO 14-50% Na₂O and/or K₂O in the total amount of  8-17%where Na₂O  0-14% and K₂O  0-15% B₂O₃  0-5% As₂O₃  0-1% Sb₂O₃  0-1% TiO₂ 0-0.2% and fluoride or fluorides substituting for the above oxide oroxides partially or entirely, a total amount of F contained in thefluoride or fluorides being 0-2%.

In another aspect of the invention, the optical glass comprises, in mass%,

SiO₂ 30-70% B₂O₃  3-20% Al₂O₃  0-6% Li₂O  0-5% Na₂O + K₂O + BaO + ZnO inthe total amount of 10-45% where Na₂O  0-13% K₂O  0-12% BaO  0-42% andZnO  0-7% PbO  0-2% TiO₂  0-0.5% As₂O₃  0-1% Sb₂O₃  0-1% and fluoride orfluorides substituting for the above oxide or oxides partially orentirely, a total amount of F contained in the fluoride or fluoridesbeing 0-11%.

In another aspect of the invention, the above described SiO₂—PbO opticalglass comprises, in mass %,

Li₂O 0-2% CaO 0-2% SrO 0-2% BaO 0-5% Al₂O₃ 0-2% the total amount of oneor more of the Li₂O, CaO, SrO, BaO and Al₂O₃ ingredients being 5% orbelow.

In another aspect of the invention, the above described SiO₂—B₂O₃optical glass comprises, in mass %,

CaO 0-2% SrO 0-2% ZrO₂ 0-2% the total amount of one or more of the CaO,SrO and ZrO₂ ingredients being 2% or below.

In another aspect of the invention, the optical glass comprises, in mass%,

P₂O₅ 4-39% Al₂O₃ 0-9% MgO 0-5% CaO 0-6% SrO 0-9% BaO 0-10% Y₂O₃ +La₂O₃ + Gd₂O₃ + Yb₂O₃ in the total amount of 0-20% Where Y₂O₃ 0-10%La₂O₃ 0-10% Gd₂O₃ 0-20% and Yb₂O₃ 0-10% TiO₂ 0-0.1% SnO₂ 0-1% As₂O₃0-0.5% Sb₂O₃ 0-0.5% AlF₃ 0-29% MgF₂ 0-8% CaF₂ 0-27% SrF₂ 0-27% BaF₂10-47% YF₃ 0-10% LaF₃ 0-10% GdF₃ 0-10% LiF 0-3% NaF 0-1% KF 0-1% thetotal amount of F in one or more of the fluorides being 10-45% and thetotal amount of one or more of MgF₂, CaF₂, SrF₂ and BaF₂ being 30-70%.

DETAILED DESCRIPTION OF THE INVENTION

First, reason for defining an amount of change in refractive index (Δn:difference in refractive index between a state before radiation and astate after radiation) caused by radiation of laser beam at wavelengthof 351 nm having average output power of 0.43 W, pulse repetition rateof 5 kHz and pulse width of 400 ns for one hour to be 5 ppm or belowwill be described.

Studies and experiments conducted by the inventors of the presentinvention have revealed that a glass which satisfies the above describedcondition, when it is exposed to radiation of ultraviolet ray of a highoutput power or continuous laser beam in a wavelength region of 300nm-400 nm, does not cause deterioration in homogeneity, distortion ordeformation in the glass surface shape due to change in refractive indexbut maintains sufficient resistance to light for use as an optical glassfor I-line and, therefore, an optical system using this glass does notdeteriorate image quality but can increase integration of LSI andimprove the exposure and copying capabilities.

Reasons for limiting the composition ranges of the respectiveingredients in the optical glass of the invention as described abovewill now be described.

In the SiO₂—PbO-alkali metal oxide glass, the SiO²⁻ ingredient is anindispensable ingredient for forming glass and can impart the glass withproperties which are peculiar to the SiO₂—PbO glass by combination withthe PbO ingredient. If the amount of this ingredient is less than 40%,refractive index tends to become excessively high and transmittancebecomes insufficient in a short wavelength region which is unsuitablefor an optical system using i-line such as an i-line exposure device. Ifthe amount of this ingredient exceeds 70%, viscosity of the glassbecomes too high with resulting difficulty in providing a homogeneousglass.

The PbO ingredient is effective for producing a high-refractive, highdispersion glass and for properly dropping viscosity of the glass. Ifthe amount of this ingredient is less than 14%, the glass becomes hardand it becomes difficult to provide a homogeneous glass. If the amountof this ingredient exceeds 50%, refractive index becomes too high and itbecomes difficult to obtain sufficiently high transmittance in a shortwavelength region.

The Na₂O and K₂O ingredients are effective for accelerate melting of theSiO₂ and PbO ingredients in glass materials and adjusting viscosity ofthe glass. If the amount of the Na₂O ingredient exceeds 14% or theamount of the K₂O ingredient exceeds 15%, it is undesirable becausechemical properties of the glass such as weather-proof property andacid-proof property are deteriorated. If the total amount of theseingredients is less than 8%, the above described effects cannot beachieved sufficiently and, therefore, viscosity of the glass becomes toohigh to obtain a homogeneous glass. If the total amount of theseingredient exceeds 17%, the chemical properties of the glass such asweather-proof property and acid-proof property are deteriorated.

The B₂O₃ ingredient may be added as an optional ingredient. Thisingredient functions as a glass forming ingredient in the same manner asthe SiO₂ ingredient. If, however, this ingredient is added in a largeamount in the SiO₂—PbO-alkali metal glass, it tends to causedeterioration in the chemical properties and, therefore, the amount ofthis ingredient should preferably be 5% or less.

The As₂O₃ and Sb₂O₃ ingredients are effective as refining aids for theglass and, besides, the As₂O₃ ingredient is effective for restrainingthe compaction phenomenon in the glass and, therefore, these ingredientsmay be added as optional ingredients. For attaining these effects,addition of each ingredient in an amount up to 1% will suffice. In acase where neither the fluorine ingredient nor the TiO₂ ingredient ispresent in the SiO₂—PbO-alkali metal oxide glass, the As₂O₃ ingredientshould be added in an amount of 0.001-1% in order to minimize the changein refractive index due to the compaction phenomenon.

The TiO₂ ingredient is effective for adjusting refractive index and Abbenumber of the glass, and restraining the compaction phenomenon andsolarization due to radiation of ultraviolet ray or laser beam of ahigh-level. If a large amount of this ingredient is added, transmittancein the short wavelength region is deteriorated and, therefore, theamount of this ingredient should preferably be 0.2% or less. In a casewhere neither the fluorine ingredient nor the As₂O₃ ingredient ispresent in the SiO₂—PbO-alkali metal glass, the TiO₂ ingredient shouldbe added in an amount of 0.001-0.2% in order to minimize the change inrefractive index due to the compaction phenomenon.

The fluorine ingredient may be added as an optional ingredient asfluoride or fluorides substituting for the above described oxide oroxides partially or entirely. This ingredient is effective forrestraining the compaction phenomenon of the glass due to radiation ofultraviolet ray or laser beam of a high level, and adjusting refractiveindex and viscosity of the glass. If the total amount of fluorinecontained in the fluoride or fluorides exceeds 2%, volatilization of thefluorine ingredient becomes excessive with resulting difficulty inproviding a homogeneous glass. In a case where neither the As₂O₃ingredient nor the TiO₂ ingredient is present in the SiO₂—PbO-alkalimetal oxide glass, the fluorine ingredient should be added in a totalamount of 0.1-2% in order to minimize the change in refractive index dueto the compaction phenomenon.

In the SiO₂—PbO-alkali metal oxide glass of the invention, the Li₂O,CaO, SrO and Al₂O₃ ingredients may be added as optional ingredients upto 2% respectively and the BaO ingredient may be added as an optionalingredient up to 5% in order to adjust viscosity, refractive index,chemical properties and stability of the glass. The total amount of oneor more of the Li₂O, CaO, SrO, Al₂O₃ and BaO ingredients should be 5% orbelow.

In the SiO₂—B₂O₃-alkali metal oxide and/or alkaline earth metal oxideglass, the SiO²⁻ ingredient is an indispensable ingredient for formingof the glass in the same manner as in the case of SiO²⁻—PbO-alkali metaloxide glass. If the amount of this ingredient is less than 30%, it isundesirable because a relatively large amount of B₂O₃ and BaOingredients is required and, moreover, refractive index becomes too highand the chemical properties are deteriorated. If the amount of thisingredient exceeds 70%, viscosity of the glass becomes too high withresulting difficulty in providing a homogeneous glass.

The B₂O₃ ingredient is, like the SiO₂ ingredient, an oxide which formsthe glass and is effective for making a low dispersion glass andadjusting viscosity of the glass. If the amount of this ingredient isless than 3%, these effects cannot be achieved sufficiently. If theamount of this ingredient exceeds 20%, it is undesirable because thechemical properties are deteriorated. The Al₂O₃ ingredient is effectivefor improving chemical properties of the glass, and adjusting viscosityand refractive index of the glass. If the amount of this ingredientexceeds 6%, viscosity of the glass becomes too high.

The Li₂O ingredient is effective for accelerating melting of glassmaterials, and it is less likely to causes decrease in refractive indexand deterioration in chemical properties than in other alkali metaloxides. If the amount of this ingredient exceeds 5%, it is undesirablebecause devitrification of the glass increases.

The Na₂O and K₂O ingredients are effective for accelerating melting ofglass materials and a stable glass can be produced even in case theseingredients are added in a large amount. If, however, the amounts of theNa₂O ingredient and the K₂O ingredient exceed 13% and 12% respectively,it is undesirable because chemical properties are deteriorated.

The BaO ingredient is effective for improving refractive index withoutexcessively increasing dispersion of the glass (i.e., withoutexcessively decreasing Abbe number) and providing a stable glass havinghigh resistivity to devitrification over a wide range of glasscomposition. If the amount of this ingredient exceeds 42%, chemicalproperties of the glass is extremely deteriorated.

The ZnO ingredient is effective for improving refractive index,adjusting viscosity and improving resistivity to devitrification. If theamount of this ingredient exceeds 7%, it is undesirable because decreasein transmittance in the short wavelength region tends to result.

For obtaining a glass which is stable, has excellent chemical propertiesand has excellent transmittance even in the short wavelength region, thetotal amount of one or more of the Na₂O ingredient, the K₂O ingredient,the BaO ingredient and the ZnO ingredient should preferably be 10-45%.

The PbO ingredient and the TiO₂ ingredient are effective for preventingsolarization in the SiO₂—B₂O₃-alkali metal oxide and/or alkaline earthmetal oxide glass. Further, the TiO₂ ingredient is effective forrestraining the compaction phenomenon. Addition of excessive amounts ofthese ingredients, however, causes deterioration in transmittance in theshort wavelength region and, therefore, the amounts of these ingredientsshould preferably be up to 2% and 0.5% respectively. In a case whereneither the fluorine ingredient nor the As₂O₃ ingredient is present inthe SiO₂—B₂O₃-alkali metal oxide and/or alkaline earth metal oxideglass, the TiO₂ ingredient should be added in an amount of 0.001-0.5%for minimizing the change in refractive index caused by the compactionphenomenon.

The As₂O₃ ingredient and the Sb₂O₃ ingredients are effective as refiningaids for the glass and, further, the As₂O₃ is effective for restrainingthe compaction phenomenon of the glass and, therefore, these ingredientsmay be added as optional ingredients. For attaining these effects,however, it will suffice if these ingredients are added up to 1%respectively. In a case where neither the fluorine ingredient nor theTiO₂ ingredient is present in the SiO₂—PbO-alkali metal oxide and/oralkaline earth metal oxide glass, the As₂O₃ ingredient should be addedin an amount of 0.001-1% for minimizing the change in refractive indexcaused by the compaction phenomenon.

The fluorine ingredient may be added as an optional ingredient asfluoride or fluorides substituting for the above described oxide oroxides partially or entirely. This ingredient is effective forrestraining the compaction phenomenon of the glass due to radiation ofultraviolet ray or laser beam of a high level, and adjusting refractiveindex and viscosity of the glass. If the total amount of fluorinecontained in the fluoride or fluorides exceeds 11%, the glass tends tobecome opaque, refractive index becomes too low and volatilization ofthe fluorine ingredient becomes excessive with resulting difficulty inobtaining a homogeneous glass. In a case where neither the As₂O³⁻ingredient nor the TiO₂ ingredient is present in the SiO₂—PbO-alkalimetal oxide glass, the fluorine ingredient should be added in a totalamount of 0.1-11% in order to minimize the change in refractive indexdue to the compaction phenomenon.

In addition to the above described ingredients, one or more of the CaOingredient, SrO ingredient and ZrO₂ ingredient may be added in a totalamount of up to 2%.

In the P₂O₅—Al₂O₃-alkaline earth fluoride glass, the P₂O₅ ingredient isa glass forming ingredient. If the amount of this ingredient is lessthan 4%, it is difficult to provide a stable glass having excellentresistivity to devitrification. If the amount of this ingredient exceeds39%, the Abbe number becomes too small and the low dispersioncharacteristic which is an advantageous feature of the composition ofthe invention becomes difficult to attain.

The Al₂O₃ ingredient is an ingredient which, by coexistence with theP₂O₅ ingredient, forms the structure of the glass and also is effectivefor improving chemical properties of the glass. If the amount of thisingredient exceeds 9%, devitrification increases.

The MgO, CaO, SrO and BaO ingredients included in the glass in the formof phosphates are beneficial for improving stability and chemicalproperties of the glass and adjusting refractive index and Abbe number.If the amounts of these ingredients exceed 5%, 6%, 9% and 10%respectively, it is undesirable because devitriifcation tends toincrease rather than decrease. For making a glass which is not likely tocause devitrification, a total amount of one or more of theseingredients should preferably be 20% or below.

The Y₂O₃, La₂O₃, Gd₂O₃ and Yb₂O₃ ingredients are effective forincreasing refractive index without decreasing the Abbe number,preventing occurrence of devitrification and improving chemicalproperties of the glass. If the amounts of these ingredients exceed 10%,10%, 20% and 10% respectively, it is undesirable because reistivity todevitrification is deteriorated. If the total amount of one or more ofthese ingredients exceed 20%, it is undesirable because resistivity todevitrification is deteriorated.

The TiO₂ ingredient is effective for improving refractive index of theglass, preventing solarization and minimaizing the change in refractiveindex due to the compaction phenomenon. For these reasons, it may beadded as required as an optional ingredient. It will suffice if thisingredient is added in an amount of 0.1% or below. Addition of thisingredient in excess of 0.1% is undesirable because it will causedeterioration in transmittance of the glass in the short wavelengthregion.

The SnO₂ ingredient is effective for improving refractive index of theglass and preventing devitrification. It will suffice if this ingredientis added in an amount of 1% or below.

The As₂O₃ ingredient and the Sb₂O₃ ingredients are effective as refiningaids for the glass and, further, the As₂O₃ is effective for restrainingthe compaction phenomenon of the glass and, therefore, these ingredientsmay be added as optional ingredients. For attaining these effects,however, it will suffice if these ingredients are added up to 0.5%respectively.

The AlF₃ ingredient is effective for decreasing dispersion of the glassand preventing devitrification. If the amount of this ingredient exceeds29%, the stability of the glass is deteriorated and crystals tend toprecipitate in the glass.

The MgF₂, CaF₂, SrF₂ and BaF₂ ingredients are effective for preventingdevitrification of the glass. If the amount of the BaF₂ ingredient isless than 10%, it becomes difficult to obtain a chemically stable glass.If the amounts of the MgF₂, CaF₂, SrF₂ and BaF₂ exceed 8%, 27%, 27% and47% respectively, devitrification increases rather than decreases. Aproper total amount of one or more of the MgF₂, CaF₂, SrF₂ and BaF₂ingredients is 30-70%.

The YF₃, LaF₃ and GdF₃ ingredients are effective for increasingrefractive index and improving resistivity to devitrification. Additionof each of these ingredients up to 10% will suffice.

The LiF, NaF and KF are effective for improving resistivity todevitrification. Addition of these ingredients in amounts exceeding 3%,1% and 1% respectively is not proper because it will increasedevitrification rather than decrease it.

In the P₂O₅—Al²⁻O₃-alkaline earth fluoride glass, it is proper that atotal amount of F contained in the fluoride or fluorides should be10-45% in order to minimize the change in refractive index of the glassdue to the compaction phenomenon. The above described oxides may besubstituted by fluorides and the above described fluorides may besubstituted by oxides within a range in which the ratio of metal ion,oxygen ion and fluorine ion of the respective oxides and fluorides ismaintained.

EXAMPLES

Examples of the optical glass made according to the invention will nowbe described. Examples No. 1 to No. 24 shown in Tables 1 to 4 areexamples of composition of the SiO₂—PbO-alkali metal oxide glass of thepresent invention. Examples No. 25 to No. 38 shown in Tables 5 and 6 areexamples of composition of the SiO₂—B₂O₃-alkali metal oxide and/oralkaline earth metal oxide glass of the present invention. Examples No.39 to 58 shown in Tables 7 to 9 are examples of composition of theP₂O₅—Al₂O₃-alkaline earth metal fluoride glass of the present invention.

Table 10 shows comparison (Comparison I and Comparison II) betweenExamples No. 59 to No. 63 of the SiO₂—PbO-alkali meal oxide glass of thepresent invention and Comparative Examples No. A and No. B of the priorart glasses.

Table 11 shows comparison (Comparison III and Comparison IV) betweenExamples No. 64 and No. 65 of the SiO₂—B₂O₃-alkali metal oxide and/oralkaline earth metal oxide glass of the present invention andComparative Examples No. C and No. D of the prior art glasses.

In Tables 1 to 11, Δn (ppm) represents an amount of change in refractiveindex between a state before radiation and a state after radiation in aportion where radiation of laser beam having beam diameter of 2.0 mm,wavelength of 351 nm, average output power of 0.43 W, pulse repetitionrate of 5 kHz and pulse width of 400 ns has been radiated for 1 hour.

Table 12 shows Examples No. 67 to No. 70 of the SiO₂—PbO-alkali metaloxide glass of the present invention and Examples No. 71 to No. 73 ofthe SiO₂—B₂O₃-alkali metal oxide and/or alkaline earth metal oxide glassof the present invention. Table 13 shows change in refractive index Δn(ppm) between a state before radiation and a state after radiation in aportion where radiation of the above-mentioned laser beam (havingwavelength of 351 nm and beam diameter of 2.0 mm) has been made on theglasses shown in Table 12 under conditions of output and radiation timewhich are different from those of Tables 1 to 11.

TABLE 1 (mass %) 1 2 3 4 5 6 7 SiO₂ 61.390 66.000 63.000 64.800 53.20055.880 50.200 PbO 24.800 19.890 20.200 18.500 34.600 30.200 38.200 Na₂O9.000 6.100 6.500 9.200 6.700 6.000 5.400 K₂O 4.000 7.700 7.900 6.7005.200 7.600 5.400 As₂O₃ 0.200 0.300 0.299 0.300 0.295 Sb₂O₃ 0.100 0.300Al₂O₃ 0.400 K₂SiF₆ 1.900 0.500 KHF₂ 0.600 TiO₂ 0.010 0.010 0.001 0.0200.005 B₂O₃ 0.500 total 100.000 100.000 100.000 100.000 100.000 100.000100.000 F 0.292 0.983 0.259 nd 1.5481 1.5317 1.5317 1.5317 1.5814 1.56731.5955 ν d 45.8 49.0 49.0 49.0 40.8 42.8 39.3 Δ n(ppm) 3.1 3.2 2.0 2.54.9 3.9 4.7

TABLE 2 (mass %) 8 9 10 11 12 13 14 SiO₂ 49.700 45.500 53.100 53.10053.100 51.995 40.000 PbO 38.200 44.900 34.700 32.700 29.700 34.00044.800 Na₂O 10.800 4.000 5.700 6.700 6.700 6.600 5.000 K₂O 4.800 3.7004.700 4.700 5.100 5.000 As₂O₃ 0.295 0.295 0.295 0.295 0.295 0.200 Sb₂O₃0.300 K₂SiF₆ 0.500 0.500 0.500 2.000 KHF₂ 1.000 0.500 B₂O₃ 5.000 TiO₂0.005 0.005 0.005 0.005 0.005 0.005 Li₂O 2.000 CaO 2.000 BaO 5.000 Total100.000 100.000 100.000 100.000 100.000 100.000 100.000 F 0.486 0.2430.259 0.259 0.259 1.035 nd 1.5955 1.6200 1.5866 1.5800 1.5801 1.57171.6258 ν d 38.7 36.3 40.9 40.8 40.9 41.7 36.9 Δ n(ppm) 4.5 4.2 4.6 4.83.9 4.6 4.5

TABLE 3 (mass %) 15 16 17 18 19 20 SiO₂ 68.95 41.00 63.00 66.00 45.0053.00 PbO 14.75 50.00 15.00 18.00 38.00 32.00 Na₂O 7.90 8.50 8.70 14.006.70 K₂O 5.40 6.00 15.00 6.00 As₂O₃ 0.30 0.30 0.30 0.20 0.30 0.30 Al₂O₃1.00 2.00 K₂SiF₆ 1.80 KHF₂ 1.20 0.20 B₂O₃ 0.50 5.00 1.70 SrO 2.00 Total100.00 100.00 100.00 100.00 100.00 100.00 F 0.58 0.10 0.93 nd 1.50941.6407 1.5171 1.5271 1.5998 1.5785 ν d 55.5 34.7 54.0 50.3 38.8 41.4 Δn(ppm) 2.3 4.5 3.3 2.5 4.6 4.6

TABLE 4 (mass %) 21 22 23 24 SiO₂ 58.80 59.74 52.64 51.65 PbO 25.0525.00 34.80 34.77 Na₂O 9.30 9.20 6.92 6.92 K₂O 4.80 4.70 4.34 5.35 As₂O₃0.20 0.20 0.10 0.10 Al₂O₃ 0.30 0.20 0.20 0.20 K₂SiF₆ 1.54 0.95 1.00 1.00TiO₂ 0.01 0.01 0.01 total 100.00 100.00 100.00 100.00 F 0.80 0.49 0.520.52 nd 1.5464 1.5470 1.5790 1.5781 ν d 45.8 45.8 40.9 41.0 Δ n(ppm) 2.92.4 4.3 3.9

TABLE 5 (mass %) 25 26 27 28 29 30 31 SiO₂ 64.950 55.850 55.350 42.00035.550 30.000 68.990 B₂O₃ 14.900 13.050 6.050 13.600 16.000 20.00011.100 Al₂O₃ 2.300 0.500 0.600 4.200 4.500 5.500 Li₂O 3.000 2.000 2.0002.000 Na₂O 9.250 1.200 0.300 0.300 9.550 K₂O 6.850 11.450 8.700 7.750BaO 16.850 37.050 40.750 40.000 1.550 ZnO 5.750 1.000 PbO 1.095 2.0000.500 TiO₂ 0.005 0.050 0.100 0.010 As₂O₃ 0.150 0.250 0.400 0.400 0.300Sb₂O₃ 0.010 0.250 0.050 K₂SiF₆ 19.090 KHF₂ 0.500 0.350 0.200 CaO 2.000Total 100.000 100.000 100.000 100.000 100.000 100.000 100.000 F 0.2439.879 0.170 0.097 Nd 1.5163 1.4875 1.5567 1.5891 1.6031 1.6056 1.5163 Nd 64.1 70.2 58.7 61.2 60.6 61.1 64.1 Δ n(ppm) 0.7 0.0 0.5 0.5 0.7 0.30.0

TABLE 6 (mass %) 32 33 34 35 36 37 38 SiO₂ 67.20 67.80 40.00 34.55 49.0055.80 35.50 B₂O₃ 3.60 4.10 12.30 18.00 17.90 13.05 16.00 Al₂O₃ 4.50 5.500.30 0.50 4.50 Li₂O 2.00 2.00 Na₂O 12.50 12.10 0.30 0.30 0.50 K₂O 6.136.15 12.00 11.40 0.20 BaO 10.22 9.45 38.00 38.75 40.80 PbO 0.50 TiO₂0.20 0.50 0.04 0.10 As₂O₃ 0.35 0.40 0.40 0.20 0.01 0.40 Sb₂O₃ 0.20K₂SiF₆ 19.20 KHF₂ 20.60 SrO 2.00 ZrO₂ 2.00 Total 100.00 100.00 100.00100.00 100.00 100.00 100.00 F 10.02 9.94 Nd 1.5184 1.5184 1.5962 1.59891.4850 1.4860 1.6025 N d 60.3 60.3 60.5 60.3 70.1 69.7 60.5 Δ n(ppm) 0.40.2 0.4 0.3 0.1 0.1 0.5

TABLE 7 (mass %) 39 40 41 42 43 44 45 46 P₂O₅ 27.45 22.45 21.05 5.5510.85 9.35 19.40 4.85 Al₂O₃ 6.55 5.35 5.05 1.35 2.60 2.20 3.95 1.15 AlF₃7.25 11.55 12.45 24.30 24.05 28.30 27.20 MgF₂ 4.45 6.05 5.10 5.20 4.255.30 4.05 CaF₂ 11.20 15.80 16.05 25.55 20.95 16.65 20.20 SrF₂ 18.0020.35 25.85 26.10 24.00 26.75 22.00 21.55 BaF₂ 25.10 18.45 14.45 11.8013.20 10.65 44.50 15.00 YF₃ 5.00 NaF 0.10 KF 0.15 1.00 Y₂O₃ 3.00 La₂O₃5.00 SnO₂ 0.05 SrO 0.80 2.10 Total 100.00 100.00 100.00 100.00 100.00100.00 100.00 100.00 F 23.97 29.37 30.32 42.60 39.28 40.94 16.30 42.94Nd 1.5296 1.5043 1.5006 1.4353 1.4505 1.4541 1.5632 1.4388 N d 76.2 79.481.1 85.5 81.6 90.5 69.8 95.1 Δ n(ppm) 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0

TABLE 8 (mass %) 47 48 49 50 51 52 53 54 P₂O₅ 25.00 38.20 22.60 20.0032.15 21.50 11.70 20.15 Al₂O₃ 6.00 8.60 5.40 1.80 3.30 2.80 2.55 AlF₃10.00 7.50 26.50 13.75 MgF₂ 0.50 2.35 8.00 4.00 4.90 CaF₂ 9.00 10.007.00 15.00 14.00 15.40 SrF₂ 15.00 14.00 20.00 9.20 13.00 23.00 15.85BaF₂ 28.00 22.00 47.00 20.00 25.00 22.00 12.00 15.80 YF₃ 3.00 LaF₃ 5.002.00 GdF₃ 10.00 2.60 LiF 2.50 Y₂O₃ 10.00 5.50 6.00 La₂O₃ 10.00 6.20Gd₂O₃ 5.00 20.00 5.00 SnO₂ 1.00 MgO 5.00 2.20 CaO 6.00 SrO 9.00 BaO 2.4010.00 As₂O₃ 0.10 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00100.00 F 12.06 16.83 17.14 22.04 22.21 23.54 36.80 28.73 Nd 1.58261.5913 1.5583 1.5783 1.5532 1.5022 1.4565 1.4973 N d 70.3 72.6 70.6 72.071.2 79.2 90.1 80.9 Δ n(ppm) 0.1 0.0 0.0 0.1 0.1 0.1 0.1 0.2

TABLE 9 (mass %) 55 56 57 58 59 P₂O₅ 4.00 25.00 25.00 11.70 24.00 Al₂O₃1.00 7.00 6.00 2.80 6.00 AlF₃ 27.00 25.50 MgF₂ 5.00 4.50 2.00 CaF₂ 21.005.00 13.50 2.00 SrF₂ 21.00 15.00 15.00 22.50 13.00 BaF₂ 16.00 19.0023.00 12.50 27.00 YF₃ 5.00 10.00 LaF₃ 5.00 10.00 5.00 NaF 1.00 Y₂O₃10.00 5.00 La₂O₃ 10.00 5.00 Gd₂O₃ 5.00 Yb₂O₃ 10.00 CaO 6.00 SrO 1.00 BaO9.00 1.00 Total 100.00 100.00 100.00 100.00 100.00 F 37.52 29.12 14.8736.59 13.13 Nd 1.4378 1.5816 1.5822 1.4562 1.5820 υd 97.1 70.2 69.9 90.070.1 Δ n(ppm) 0.1 0.1 0.2 0.1 0.1

TABLE 10 (mass %) Comparison I Comparison II 59 60 Com. Ex. A 61 62 63Com. Ex. B SiO₂ 63.00 65.30 66.00 53.10 53.05 52.00 53.10 PbO 20.2018.50 19.90 34.70 34.70 34.00 34.70 Na₂O 6.50 9.20 6.10 6.70 6.70 6.606.70 K₂O 7.90 6.70 7.70 5.20 5.20 5.10 5.20 As₂O₃ 0.30 0.30 0.30 Sb₂O₃0.10 0.30 0.30 0.30 Al₂O₃ 0.40 K₂SiF₆ 1.90 2.00 TiO₂ 0.05 total 100.00100.00 100.00 100.00 100.00 100.00 100.00 F 0.98 1.04 Nd 1.5317 1.53171.5317 1.5786 1.5801 1.5717 1.5800 ν d 49.0 49.0 49.0 41.0 40.9 41.740.8 Δ n(ppm) 2.9 3.4 6.3 4.9 4.5 4.2 10.0

TABLE 11 (mass %) Comparison III Comparison IV 64 Com. Ex. C 65 Com. Ex.D SiO₂ 67.80 67.20 68.99 64.95 B₂O₃ 4.10 3.60 11.10 14.90 Al₂O₃ 2.30Na₂O 12.10 12.50 9.55 9.25 K₂O 6.15 6.13 7.75 6.85 BaO 9.45 10.22 1.55ZnO 1.00 PbO 1.60 TiO₂ 0.20 0.01 Sb₂O₃ 0.20 0.35 0.05 0.15 Total 100.00100.00 100.00 100.00 Nd 1.5184 1.5184 1.5163 1.5163 ν d 60.3 60.3 64.164.1 Δ n(ppm) 0.2 6.0 0.0 7.0

TABLE 12 (mass %) No. 66 67 68 69 70 71 72 SiO₂ 63.20 65.48 51.62 51.6257.85 68.50 69.34 B₂O₃ 13.52 3.99 11.11 PbO 20.33 20.27 34.80 34.80 K₂O7.96 7.79 5.35 5.35 11.85 6.00 7.76 Na₂O 6.51 6.18 6.93 6.92 11.85 9.55Al₂O 0.37 0.20 0.20 0.50 K₂SiF₆ 1.53 1.00 1.00 16.23 As₂O₃ 0.28 0.100.10 0.01 0.20 0.03 Sb₂O₃ 0.10 TiO₂ 0.01 0.04 0.20 0.01 BaO 9.26 1.19ZnO 1.01 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 F 0.790.52 0.52 8.40 nd 1.53168 1.53145 1.57904 1.57807 1.48713 1.518201.51593 ν d 48.9 49.0 40.9 41.0 70.2 60.3 64.1

TABLE 13 No. Average (mass %) Output Δ n (ppm) Power(W) Time 66 67 68 6970 71 72 0.10 165 hrs 0.2 0.60 10 min. 0.3 0.60 15 min. 0.3 0.60 30 min.0.5 0.60 1 hour 0.5 0.60 10 min. 0.6 0.60 1 hour 1.1 2.00 10 min. 0.71.20 15 min. 1.0 2.00 25 min. 1.6 2.00 10 min. 0.5 1.20 15 min. 0.8 2.0025 min. 1.3 1.50 3 hrs 0.0 2.65 3 hrs. 0.5 2.65 3 hrs. 0.6

As shown in Tables 1 to 12, the amount of change Δn in a period betweenbefore and after radiation of laser beam in the glasses of Examples No.1 to No. 73 is 5 ppm or below. The glasses of Examples No. 60 to No. 66shown in Tables 10 and 11 all have a smaller amount of change (Δn) in aperiod between before and after radiation of laser beam than the priorart glasses of Comparative Examples No. A to No. D which have similarcontents of SiO₂, PbO, B₂O₃, alkali metal oxide and BaO as well assimilar values of nd and νd to these Examples of the invention and,thus, show the advantageous effects of containing the fluorineingredient and/or the titanium oxide ingredeint and/or the arsenic oxideingredient.

The glasses of the above described examples of the invention can beeasily manufactured by weighing and mixing optical glass materials suchas oxides, carbonates, nitrates, hydroxides, phosphates and fluorides,melting the materials at 900-1500° C. for about 3 hours to 10 hours in aplatinum container and/or a quartz container and thereafter refining,stirring, and homogenizing the melt and cooling the melt to apredetermined temperature, and casting it in a preheated mold andannealing it.

In summing up, the optical glass of the present invention is an opticalglass wherein an amount of change in refractive index (Δn: difference inrefractive index between a state before radiation and a state afterradiation) caused by radiation of laser beam at wavelength of 351 nmhaving average output power of 0.43 W, pulse repetition rate of 5 kHzand pulse width of 400 ns for one hour is 5 ppm or below.

It is also an optical glass comprising a fluorine ingredient and/or atitanium oxide ingredient and/or an arsenic oxide ingredient. It is alsoa SiO₂—PbO-alkali metal oxide glass containing a fluorine ingredientand/or a titanium oxide ingredient and/or an arsenic oxide ingredientrespectively of a specific composition range, or a SiO₂—B₂O₃-alkalimetal oxide and/or alkaline earth metal oxide glass containing afluorine ingredient and/or a titanium oxide ingredient and/or an arsenicoxide ingredient respectively of a specific composition range, or aP₂O₅—Al₂O₃-alkaline earth metal fluoride glass containing a fluorineingredient and/or a titanium oxide ingredient and/or an arsenic oxideingredient respectively of a specific composition range. In the opticalglasses of the present invention, an amount of change (Δn) in refractiveindex in a portion where ultraviolet ray or laser beam of a wavelengthin the range from 300 nm to 400 nm having a high level has been radiatedis very small. Accordingly, by using the optical glass of the presentinvention in a high-precision optical system using light of a highenergy density such as high level ultraviolet ray and laser beam in thewavelength reion of 300 nm to 400 nm, deterioration in homogeneity ofthe glass, increase in distortion in the image or deformation in thesurface shape of the glass hardly takes place and, therefore distortionor bleeding in the image hardly takes place. For these reasons, theoptical glass of the invention is very useful. By using, for example,the optical glass of the invention for lenses of an optical system orlighting system of an i-line stepper, exposure and copying of a highlyintegrated LSI pattern can be made with a high resolution.

1. An optical glass having optical constants of a refractive index (nd)within a range from 1.49 to 1.6, comprising, in mass %, P₂O₅  4-39%Al₂O₃  0-9% MgO  0-5% CaO  0-6% SrO  0-9% BaO  0-10% Y₂O₃ + La₂O₃ +Gd₂O₃ + Yb₂O₃  0-20% in the total amount of Where Y₂O₃  0-10% La₂O₃ 0-10% and Yb₂O₃  0-10% TiO₂  0-0.1% SnO₂  0-1% As₂O₃  0-0.5% Sb₂O₃ 0-0.5% AlF₃  0-29% MgF₂  0-8% CaF₂  0-27% SrF₂  0-27% BaF₂ 10-47% YF₃ 0-10% LaF₃  0-10% GdF₃  0-10% LiF  0-3% NaF  0-0.1% KF  0-1% the totalamount of F in one or more of the fluorides being 22-45% and the totalamount of one or more of MgF₂, CaF₂, SrF₂ and BaF₂ being 30-70%.


2. An optical glass as defined in claim 1 wherein an amount of change inrefractive index (Δn: difference in refractive index between a statebefore radiation and a state after radiation) caused by radiation oflaser beam at wavelength of 351 nm having average output power of 0.43W, pulse repetition rate of 5 kHz and pulse width of 400 ns for one houris 5 ppm or below.
 3. An optical glass having optical constants of anAbbe number (νd) within a range from 69 to 82, comprising, in mass %,P₂O₅  4-39% Al₂O₃  0-9% MgO  0-5% CaO  0-6% SrO  0-9% BaO  0-10% Y₂O₃ +La₂O₃ + Gd₂O₃ + Yb₂O₃ in the total amount of  0-20% Where Y₂O₃  0-10%La₂O₃  0-10% and Yb₂O₃  0-10% TiO₂  0-0.1% SnO₂  0-1% As₂O₃  0-0.5%Sb₂O₃  0-0.5% AlF₃  0-29% MgF₂  0-8% CaF₂  0-27% SrF₂  0-27% BaF₂ 10-47%YF₃  0-10% LaF₃  0-10% GdF₃  0-10% LiF  0-3% NaF  0-0.1% KF  0-1% thetotal amount of F in one or more of the fluorides being 22-45% and thetotal amount of one or more of MgF₂, CaF₂, SrF₂ and BaF₂ being 30-70%.


4. An optical glass as defined in claim 3 wherein an amount of change inrefractive index (Δn: difference in refractive index between a statebefore radiation and a state after radiation) caused by radiation oflaser beam at wavelength of 351 nm having average output power of 0.43W, pulse repetition rate of 5 kHz and pulse width of 400 ns for one houris 5 ppm or below.
 5. An optical glass having optical constants of anAbbe number (νd) within a range from 95.1 to 97.1, comprising, in mass%, P₂O₅  4-39% Al₂O₃  0-9% MgO  0-5% CaO  0-6% SrO  0-9% BaO  0-10%Y₂O₃ + La₂O₃ + Gd₂O₃ + Yb₂O₃ in the total amount of  0-20% Where Y₂O₃ 0-10% La₂O₃  0-10% and Yb₂O₃  0-10% TiO₂  0-0.1% SnO₂  0-1% As₂O₃ 0-0.5% Sb₂O₃  0-0.5% AlF₃  0-28.3% MgF₂  0-8% CaF₂  0-27% SrF₂  0-27%BaF₂ 10-47% YF₃  0-10% LaF₃  0-10% GdF₃  0-10% LiF  0-3% NaF  0-1% KF 0-1% the total amount of F in one or more of the fluorides being 10-45%and the total amount of one or more of MgF₂, CaF₂, SrF₂ and BaF₂ being30-70%.


6. An optical glass as defined in claim 5 wherein an amount of change inrefractive index (Δn: difference in refractive index between a statebefore radiation and a state after radiation) caused by radiation oflaser beam at wavelength of 351 nm having average output power of 0.43W, pulse repetition rate of 5 kHz and pulse width of 400 ns for one houris 5 ppm or below.
 7. A method of providing an optical glass for lensesof an optical system of an i-line stepper, said method comprisingutilizing in said i-line stepper a lens made from an optical glasscomprising, in mass %, P₂O₅  4-39% Al₂O₃  0-9% MgO  0-5% CaO  0-6% SrO 0-9% BaO  0-10% Y₂O₃ + La₂O₃ + Gd₂O₃ + Yb₂O₃ in the total amount of0-20% Where Y₂O₃  0-10% La₂O₃  0-10% Gd₂O₃  0-20% and Yb₂O₃  0-10% TiO₂ 0-0.1% SnO₂  0-1% As₂O₃  0-0.5% Sb₂O₃  0-0.5% AlF₃  0-29% MgF₂  0-8%CaF₂  0-27% SrF₂  0-27% BaF₂ 10-47% YF₃  0-10% LaF₃  0-10% GdF₃  0-10%LiF  0-3% NaF  0-1% KF  0-1% the total amount of F in one or more of thefluorides being 10-45% and the total amount of one or more of MgF₂,CaF₂, SrF₂ and BaF₂ being 30-70%.